Queries can become quite complex and, especially when combined with
different analyzers and field mappings, can become a bit difficult to follow.
The validate-query API can be used to check whether a query is valid.

Using the explain parameter has the added advantage of returning
a human-readable description of the (valid) query, which can be useful for
understanding exactly how your query has been interpreted by Elasticsearch:

From the explanation, you can see how the match query for the query string
really powerful has been rewritten as two single-term queries against
the tweet field, one for each term.

Also, for the us index, the two terms are really and powerful, while
for the gb index, the terms are realli and power. The reason
for this is that we changed the tweet field in the gb index to use the
english analyzer.